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National Instruments NI PXI-7831R Common-Mode Signal Rejection Considerations

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Chapter 2 Hardware Overview ofthe NI PXI-7831R

© National Instruments Corporation 2-13 NI PXI-7831R User Manual

amplifier, and the signal local ground reference is connected to the negative

input of the instrumentation amplifier. The ground point of the signal

should, therefore, be connected to AISENSE. Any potential difference

between the NI PXI-7831R ground and the signal ground appears as a

common-mode signal at both the positive and negative inputs of the

instrumentation amplifier, and this difference is rejected by the amplifier.

If the input circuitry of a NI PXI-7831R were referenced to ground, in this

situation as in RSE input mode, this difference in ground potentials would

appear as an error in the measured voltage.

Figure 2-8 shows how to connect a grounded signal source to a channel on

the NI PXI-7831R configured for NRSE input mode.

Figure 2-8. Single-Ended Input Connections for Ground-Referenced Signals

Common-Mode Signal Rejection Considerations

Figures 2-5 and 2-8 show connections for signal sources that are already

referenced to some ground point with respect to the NI PXI-7831R.

In these cases, the instrumentation amplifier can reject any voltage caused

by ground potential differences between the signal source and the device.

In addition, with differential input connections, the instrumentation

amplifier can reject common-mode noise pickup in the leads connecting the

signal sources to the device. The instrumentation amplifier can reject

NRSE Input Mode Selected

–

+

–

+

–

+

–

+

Vcm

Vs

Ground-

Referenced

Signal

Source

Common-

Mode

Noise and

Ground

Potential

I/O Connector

AISENSE

AIGND

VmMeasured

Voltage

Instrumentation

Amplifier

x8 Channels

AI+

AI–

Contents

Main Page Important Information Warranty Copyright Trademarks Patents Compliance FCC/Canada Radio Frequency Interference Compliance Determining FCC Class FCC/DOC Warnings Class A Contents About This Manual Chapter 1 Introduction Chapter 2 Hardware Overview of the NI PXI-7831R Page About This Manual Conventions Reconfigurable I/O Documentation Related Documentation Introduction About the Reconfigurable I/O Devices Using PXI with CompactPCI What You Need to Get Started Getting Started with Windows 2000/XP Getting Started with the RT Module Overview of Reconfigurable I/O Reconfigurable I/O Concept Flexible Functionality User-Defined I/O Resources Device-Embedded Logic and Processing Reconfigurable I/O Architecture Page Reconfigurable I/O Applications Software Development FPGA Module RT Module Cables and Optional Equipment Custom Cabling Unpacking Safety Information Page Page National Instruments Corporation 2-1 NI PXI-7831R User Manual Hardware Overview of the NI PXI-7831R PXI/CompactPCI Bus Figure 2-1. NIPXI-7831R Block Diagram + Calibration DACs Analog Input Input Modes Input Range Connecting Analog Input Signals Types of Signal Sources Floating Signal Sources Ground-Referenced Signal Sources Input Modes Figure 2-4. Summary of Analog Input Connections Differential Connection Considerations (DIFF Input Mode) Differential Connections for Ground-Referenced Signal Sources Differential Connections for Nonreferenced or Floating Signal Sources Page Single-Ended Connection Considerations Single-Ended Connections for Floating Signal Sources (RSE Input Mode) Single-Ended Connections for Grounded Signal Sources (NRSE Input Mode) Common-Mode Signal Rejection Considerations Analog Output Connecting Analog Output Signals Digital I/O Connecting Digital I/O Signals Page Page PXI Trigger Bus PXI Local Bus Switch Settings Power Connections Field Wiring Considerations Page Calibration Loading Calibration Constants Internal Calibration External Calibration A Specifications Analog Input Input Characteristics Accuracy Information DC Transfer Characteristics Dynamic Characteristics Analog Output Output Characteristics Accuracy Information DC Transfer Characteristics Voltage Output Dynamic Characteristics Digital I/O Reconfigurable FPGA Calibration Bus Interface Power Requirement Physical Maximum Working Voltage Environmental Safety Electromagnetic Compatibility CE Compliance B Connecting I/O Signals Page Appendix B Connecting I/O Signals National Instruments Corporation B-3 NI PXI-7831R User Manual Figure B-2. NIPXI-7831R I/O Connector Pin Assignments DIO Connector Pin Assignment MIO Connector Pin Assignment Caution Connections that exceed any of the maximum ratings of input or output signals Table B-1. I/O Connector Signal Descriptions Connecting to 5B and SSR Signal Conditioning Table B-2. NIPXI-7831R I/O Signal Summary Page Figure B-3. Connector Pinouts When Using NSC68-262650 Cable AO 07 Connector AI 07 Connector DIO 015 Connector Figure B-4. Connector Pinouts When Using the NSC68-5050 Cable DIO 023 Connector DIO 2439 Connector C Using the SCB-68 Shielded Connector Block Appendix C Using the SCB-68 ShieldedConnector Block NI PXI-7831R User Manual C-2 ni.com Quick Reference Label S5 S4 S1 Figure C-2. SCB-68 Quick Reference Label for the NIPXI-7831R Technical Support and Professional Services Page Glossary Numbers/Symbols A B C D Page I L M N O P R S T V W